A well known maintenance procedure in ship overhaul work requires the removal or cleaning, and then the replacement of frequent intervals, of ships' hull bottom antifouling (AF) paints which are used to prevent attachment and progressive growth of sea life. Operating requirements of todays high speed Navy have imposed severe demands on ships coating systems, especially on antifouling paints. Fuel conservation, high speed capabilities, and extended periods between ship drydockings are Naval objectives which depend to a great extent on the performance of antifouling (AF) paints.
The best known prior art antifouling paints were the old stand-by cuprous oxide paints which operate on the principle of leaching out, at a controlled rate, a toxic solution to kill or discourage sea life from attaching to the ships' bottom. The cuprous oxide paints leached at a high rate in order to perform their function, and therefore had to be mechanically removed and renewed at frequent intervals. For example, one could expect an effective life of only six to 18 months, thus, one had to accept the low efficiency of a "dirty bottom" or the "down time" of drydocking.
To overcome these difficulties, and to achieve the desired objectives discussed above, the old cuprous oxide AF paints are being rapidly replaced by new, improved AF paints and coatings containing organo-metallic compounds, such as for example, tributyl tin oxide (TBTO), tributyl tin fluoride (TBTF), tripropyl tin oxide (TPrTO), and tripropyl tin fluoride (TPrTF), etc. Also, toxic organo-metallic compounds of lead and other heavy metals, such as for example, triphenyl lead acetate, may be used. The advantage of these new organo-metalic AF paints over the previous cuprous oxide type AF paints is that they are far more toxic to sea life and can be designed with very low leach rates to perform their AF function. Their antifouling life may thus be prolonged to a projected five year period. However, ships' hulls bearing these organo-metallic AF coatings do eventually require abrasive blasting to facilitate repainting. Since these organo-metallic compounds, particularly the commonly used organo-tins, are not biodegradable, remain toxic for long periods, are approximately 20 times more toxic than cuprous oxide, they therefore cannot be allowed to contaminate the water environment i.e., harbor, and disposal of the spent abrasive material containing these paint residues has become a serious problem of growing proportions.
The current shipyard practice for disposal of spent abrasive materials containing organo-tin AF paint residues involves shoveling or otherwise collecting the material from the floor of the drydock into 55 gallon metal drums which are then sealed and transported to designated class 1 landfill sites for burial. A class 1 landfill offers minimal seepage risks. This procedure is unsatisfactory because: (1) a class 1 landfill is not always available. For example, Hawaii does not have a class 1 landfill. Tons of the contaminated spent abrasive have therefore accumulated at Pearl Harbor awating shipment to the mainland states for disposal, (2) the period over which the material remains toxic while underground has not been established. It is known that organo-tin compounds degrade under the influence of ultra violet light from sunlight and by the action of some soil bacteria. However, packaging the material in metal drums effectively shields the organo-tin compounds from both the ultra violet and the soil bacteria. (3) The process does not really solve the pollution problem. It only transfers the pollutant from one environment to another. (4) The process serves to concentrate the pollutant into discrete areas or pockets beneath the ground. This could cause problems in the future.